Secondary battery

ABSTRACT

A secondary battery includes a can into which an electrode assembly is inserted, a cap assembly mounted to an opening of the can; and an electolyte injection hole formed on at least one of the can and cap assembly, and safety member to close the electolyte injection hole. The electolyte injection hole is formed on a negative portion of the cap assembly. The safety member is inserted into and welded on the electolyte injection hole.

TECHNICAL FIELD

The present invention relates to a secondary battery and, moreparticularly, a safety system of a secondary battery which can reduceinternal pressure thereof to prevent the explosion of the secondarybattery.

BACKGROUND ART

Generally, a secondary battery is a rechargeable battery such as anickel-metal hydride battery, a lithium battery or a lithium-ion batterywhich is widely used in many applications. Such a secondary battery issubject to high internal pressures due to gases generated by chemicalreactions when it is discharged and recharged. Though not common, it ispossible for the battery to explode as a result of the gases produced.

Therefore, many presently known secondary batteries have a cap assemblyprovided with a safety valve which can discharge gases through adischarge hole formed on a cap cover so as to reduce the pressure in thebatteries when the pressure in the battery is excessively raised.

The lithium-ion battery comprises an electrode assembly inserted into acap. A cap assembly is mounted on an upper end of the can. Electrolyteis injected into the can through an inlet port formed on the capassembly. Insulating members are disposed between the electrode assemblyand the can.

Referring to FIG. 3, there is shown a conventional cap assembly 2. Thecap assembly 2 comprises a negative portion 4 welded on an upper end ofthe can, a positive portion 6 disposed on a central portion of thenegative portion 4, and an insulating plate 8 disposed between thenegative portion 4 and positive portion 6. A rivet 10 penetrates throughthe negative potion 4 and positive portion 6 is coupled to the positiveelectrode of the roll electrode assembly.

In the above described conventional lithium-ion battery, if the pressurewithin the battery is abruptly increased by the gas generated therein,the battery may explode. Thus, there is provided gas release means inthe secondary battery.

That is, safety grooves 12 are formed in the negative portion 4 of thecap assembly 2 through a mechanical process, etching or electroformingprocess. The safety grooves 12 are broken open when the internalpressure of the battery is increased above a predetermined level,thereby preventing the battery from exploding.

An electrolyte injection hole 14 is formed on the negative portion 4 ofthe cap assembly 2. After the electrolyte is injected through the hole14, a plug 16 is snugly fitted into the hole 14 and is then welded toprovide a seal.

FIG. 4 shows another example of a conventional cap assembly 2.

In this example, a ball(not shown) is inserted into the injection hole14 and is then welded to provide a seal.

In the above described conventional cap assembly shown in FIGS. 3 and 4,since the safety grooves and the electrolyte injection hole are formedon the negative portion which is small in size, it is difficult todesign and manufacture the same.

In the conventional cap assembly shown in FIG. 4, since the diameter ofthe injection hole is small, it is difficult to inject electrolyte intothe can.

DISCLOSURE OF INVENTION

Therefore, the present invention has been made in an effort to solve theabove described drawbacks of the prior art.

It is an object of the present invention to provide a cap assembly for asecondary battery, in which safety means can precisely operate at apre-set pressure to prevent the battery from exploding.

It is another object of the present invention to provide a cap assemblyin which the safety means can be easily formed, thereby reducingmanufacturing costs.

To achieve the above objects, the present invention provide a secondarybattery comprising a can into which an electrode assembly is inserted; acap assembly mounted to an opening of the can; and an electrolyteinjection hole formed on at least one of the can and cap; and a safetymember mounted to tightly close the electrolyte injection hole.

Preferably, the electrolyte injection hole is formed on a negativeportion of the cap assembly.

Preferably, the safety member is inserted into and welded on theelectrolyte injection hole.

Alternatively, the safety member is disposed on the electrolyteinjection hole and is welded on the negative portion.

Preferably, the safety member is made of a material selected from thegroup consisting of aluminum, nickel, stainless steel, and nickelgilding steel plate.

Preferably, the safety member is designed to be broken by battery ofabout 10 to 30 kgf/cm².

Alternatively, the safety member is provided with a plurality ofgrooves.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof present invention and wherein:

FIG. 1 is a cross sectional view illustrating a secondary battery wherea cap assembly according to a preferred embodiment of the presentinvention is employed;

FIG. 1A is a cross sectional view illustrating a secondary battery wherea cap assembly according to another preferred embodiment of the presentinvention is employed.

FIG. 2 is a plane view illustrating a cap assembly of a secondarybattery according to a preferred embodiment of the present invention;

FIG. 3 is a plane view illustrating a conventional cap assembly of asecondary battery; and

FIG. 4 is a plane view illustrating another conventional cap assembly ofa secondary battery.

BEST MODE FOR CARRYING OUT THE INVENTION

The following is the description of the preferred embodiments accordingto the present invention. In the drawing, like reference numerals havebeen used to identify like elements in each figure.

Referring first to FIGS. 1 and 2, there are respectively shown asectional view of a secondary battery where a cap assembly 24 accordingto the present invention is employed and a plane view of the capassembly 24.

The cap assembly 24 of the present invention is coupled on an upper endof a can 22 in which a roll electrode assembly 20 consisting of apositive electrode, a negative electrode, and a separator, andelectrolyte are received. The can 22 contacts the negative electrode 21by a tap 38 a.

Insulating plates 26 are provided at upper and lower ends of theelectrode assembly 20 to prevent the electrode assembly 20 fromcontacting the cap assembly 24 and the can 22.

The cap assembly 24 comprises a negative portion 28 which is welded tothe upper end of the can 22, a positive portion 32 formed on a centralportion of the negative portion 28, and a rivet 34 mounted penetrating acentral portion of the negative portion 28 and positive portion 32. Aninsulating member 30 is disposed between the negative portion 28 andpositive portion 32. The rivet 34 is used as coupling means for couplingthe positive portion 32 with the negative portion 28. An insulatingmember 36 is disposed between the rivet 34 and the negative portion 28.The rivet 34 is connected to the positive electrode of the electrodeassembly through a tap 38. That is, the rivet is used as a terminal forconnecting the positive electrode to the positive portion 32. Anelectrolyte injection hole 40 is formed on the negative portion 28 toinject electrolyte into the can.

Although, in this embodiment, an electolyte injection hole 40 is formedon the negative portion 28, the location of the electrolyte injectionhole 40 is not limited to this structure but can be formed on the can22, as illustrated in FIG. 1A.

After the electrolyte is injected into the can 22, the injection hole 40is tightly closed by a safety plate 42. In this embodiment, the safetyplate 42 may be formed having the same size as that of the injectionhole and inserted into and welded on the injection hole 40.

Alternatively, the safety plate 42 may be formed having the larger sizeas that of the injection hole 40 and is positioned to cover theinjection hole 40. The safety plate 42 positioned on the injection hole40 is welded on the negative portion 28.

The safety plate 42 is for preventing the explosion of the battery. Thatis, The safety plate 42 is formed having the thickness or rigidity lessthan that of the negative portion 28.

Alternatively, in the case where the safety plate 42 is made in the samematerial as the negative portion 28, safety grooves 44 are formed on thesafety plate 42 through a mechanical process, etching or electroformingprocess. The safety plate 42 is broken open when the internal pressureof the battery is increased above a predetermined level, therebypreventing the battery from exploding.

More in detail, the safety plate 42 may be made of a material selectedfrom the group consisting of aluminum, nickel, stainless steel, andnickel gilding steel plate.

Preferably, the safety plane 42 is designed to be broken by the internalpressure of about 10 to 30 kgf/cm².

Therefore, when the internal pressure of the battery is increased abovea predetermined level by gas generated when the battery is charged anddischarged, the safety plate 42 is removed or cracked, thereby enablinggas from the battery to be exhausted to reduce the internal pressure.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to understood that the invention is not limited to the disclosedembodiment, but, on the contrary is intended to cover variousmodifications and equivalent arrangements and methods included withinthe spirit and scope of the appended claims.

What is claimed is:
 1. A secondary battery, comprising: a can; a cap assembly on an end of the can; an electrolyte injection hole formed on the can; and a safety member to close the electrolyte injection hole, the safety member for reducing an internal pressure in the can once the internal pressure exceeds a predetermined level.
 2. The secondary battery of claim 1, further comprised of the can being coupled to a negative electrode of an electrode assembly for the secondary battery.
 3. The secondary battery of claim 1, further comprised of the safety member being inserted into and welded on the electrolyte injection hole.
 4. The secondary battery of claim 1, further comprised of the safety member being disposed on the electrolyte injection hole and being welded on the can, the can being coupled to a negative electrode of an electrode assembly for the secondary battery.
 5. A secondary battery, comprising: a can; a cap assembly on an end of the can; an electrolyte injection hole formed on the can; and a safety member to close the electrolyte injection hole, the safety member being made of a material selected from the group consisting of aluminum, nickel, stainless steel, and nickel gilding steel plate.
 6. A secondary battery, comprising: a can; a cap assembly on an end of the can; an electolyte injection hole formed on the can; and a safety member to close the electrolyte injection hole, the safety member being designed to be broken by battery pressure of about 10 to 30 kgf/cm².
 7. A secondary battery, comprising: a can; a cap assembly on an end of the can; an electrolyte injection hole formed on the can; and a safety member to close the electrolyte injection hole, the safety member being provided with a plurality of grooves.
 8. The secondary battery of claim 7, further comprised of the safety member being inserted into and welded on the electrolyte injection hole.
 9. The secondary battery of claim 7, further comprised of the safety member being disposed on the electrolyte injection hole and being welded on the can, the can being coupled to a negative electrode of an electrode assembly for the secondary battery.
 10. The secondary battery of claim 7, further comprised of the safety member being made of a material selected from the group consisting of aluminum, nickel, stainless steel and nickel gilding steel plate.
 11. The secondary battery of claim 7, further comprised of the safety member being designed to be broken by battery pressure of about 10 to 30 kgf/cm². 